Uniform basis weight self-bonded nonwoven webs and a process for making such webs are disclosed in U.S. patent application Ser. No. 556,353, now U.S. Pat. No. 5,173,356, filed on Jul. 20, 1990, in the name of G. M. Eaton, et.al., assigned to the present assignee. Composites of such self-bonded nonwoven webs with materials such as meltblown fabric, woven fabric, porous film and net-like webs such as those designated CLAF.RTM. and available from Amoco Nisseki CLAF, Inc., are disclosed, respectively, in U.S. Pat. No. 5,073,436, U.S. patent application Ser. No. 805,579, filed Dec. 10, 1991, in the name of A. W. Stahle, et al., U.S. patent application Ser. No. 601,519, filed Oct. 23, 1990, in the name of W. H. Stover, and U.S. patent application Ser. No. 602,519, now U.S. Pat. No. 5,182,162, filed Oct. 24, 1990, in the name of F. G. Andrusko, each assigned to the present assignee.
These self-bonded nonwoven webs provide desirable properties of uniform basis weight and coverage and may be used as nonwoven webs by themselves or in combination with other materials in the form of composites. However, for applications wherein such self-bonded nonwoven webs can come into contact with a person's skin, it has been found desirable that these self-bonded webs have improved softness and antistatic properties.
Plastics, having insulative properties, are quite receptive to static electricity and typically do not dissipate static charge unless modified. Additives or modifiers which can be added to plastic melts or applied to plastics to prevent the buildup of electrostatic charges on plastic surfaces of articles made from such articles are referred to as "antistatic agents" or "antistats". Various antistat compositions are disclosed in the patents discussed below.
U.S. Pat. No. 3,580,735 discloses incorporating at least one antistatic agent such as quaternary ammonium salts, glycerides or fatty acid amides with at least one inorganic modifier and treating shaped articles with an antistatic agent for external use, such as a vinyl polymer containing an alkyl, carboxyl, glycidyl or sulphone group.
Japanese Patent No. 60-058444 discloses polyolefin compositions having 0.05 to 1.0 parts by weight of alkyl amines and/or alkylamides and 0.1 to 2.0 parts by weight of glycerine monoesters such as glycerine monostearate and linolic acid monoglyceride wherein such compositions have excellent antistatic properties and which, even when heat molded, high speed injection molded or oriented, do not lose the antistatic effect.
Belgium Patent No. 901310 discloses polypropylene compositions for fiber production containing synergistic mixtures of glycerol monostearate and ethoxylated tertiary amine.
Czechoslovakian Patent No. 8601268 discloses glycerol monostearate as an antistatic agent for polyolefins such as polypropylene fibers.
U.S. Pat. No. 4,041,203 discloses a nonwoven fabric-like material comprising a web of substantially continuous and randomly deposited, molecularly oriented filaments of a thermoplastic polymer having an average filament diameter in excess of 12 microns and an integrated mat of discontinuous, thermoplastic polymeric microfibers having an average fiber diameter up to about 10 microns and a softening temperature of about 10.degree. to 40.degree. C. less than the softening temperature of the continuous filaments. The disclosed laminates are treated with antistatic compositions in order to reduce surface resistivity to below about 1.times.10.sup.12 ohms/square.
U.S. Pat. No. 5,071,699 discloses antistatic flexible fabric material formed from woven, axially oriented polypropylene yarn wherein the fabric has a coating on one or both sides of the fabric of a flexible thermoplastic polymer containing about 0.2 to 8 wt% of a polyol ester of a C.sub.10 to C.sub.28 fatty acid. The polypropylene yarn used to form the fabric may optionally also contain a lesser amount of the polyol ester of a C.sub.10 to C.sub.28 fatty acid.
When present on thermoplastic self-bonded nonwoven webs, static electricity can create undesirable effects such as dust pickup, interference during processing of such webs, static cling, sparking, and the like. In view of these undesirable effects, there is a need for uniform basis weight self-bonded, fibrous nonwoven webs having improved antistatic properties and whereby these nonwoven webs and composites comprising such webs have a reduced clinging effect and elimination of spark discharge and are less attractive to dust and lint. It is also desirable that for applications having human skin contact the self-bonded webs prepared from polypropylene-based thermoplastic resins have improved softness. Likewise, it is desirable especially in composite applications that such polypropylene-based webs which have antistatic agents present retain their as-formed water resistance properties as measured by hydrostatic resistance and water impact penetration.
Accordingly, it is an object of this invention to provide uniform basis weight self-bonded, fibrous nonwoven web having improved antistatic and surface resistivity properties.
Another object of this invention is to provide a uniform basis weight self-bonded, fibrous nonwoven web having improved antistatic and softness properties comprising a plurality of substantially continuous polymeric filaments wherein the polymeric filaments comprise a polyol ester of a monocarboxylic acid having 10 to 28 carbon atoms and a thermoplastic.
A still further object of this invention is to provide a composite product having antistatic properties, softness and retention of water resistance properties comprising at least one layer of a uniform basis weight self-bonded, fibrous nonwoven web comprising a plurality of substantially randomly disposed, substantially continuous polymeric filaments comprising glycerol monostearate and a thermoplastic selected from the group consisting of polypropylene, ethylene-propylene random copolymer, a blend of polypropylene and polybutene, and a blend of polypropylene and linear low density polyethylene wherein said web has a Basis Weight Uniformity Index of 1.0.+-.0.05 determined from average basis weights having standard deviations of less than 10% and said web is adhered to at least one layer of a material selected from the group consisting of porous film, impervious film, woven fabric, polymeric foam product and nonwoven fabric such as meltblown fabric, spunbond fabric and carded web fabric.